A method of calibrating the audiometric TDH‐39 earphone is developed that eliminates the requirement for expensive calibration equipment. This form of reciprocity calibration has been examined and evaluated for 25 pairs of TDH‐39 earphones. Two earphones of a headset are alternately used as transmitters and receivers, acoustically coupled in a small cavity. The electrical, acoustical, and mechanical constants of the transducers are then combined using the absolute averages of the sensitivities of the earphones, where the absolute sensitivity is traceable to the National Bureau of Standards. These sensitivity averages are then integrated with the transmitter‐receiver voltage transfer characteristic to obtain a calibrating K factor. The calibrating K factor enables field determination of average sensitivity. By use of a third earphone it is possible to extend the analysis to determine the absolute sensitivity of any one of the three earphones.